As defined, blood pressure is the pressure exerted by the blood against the inner walls of the blood vessel, especially the arteries. Also, heart can receive blood from the veins and pump it through the arteries by alternate dilation and contraction. As such, pressure can be expressed as either contraction pressure (i.e., pressure exerted by the blood pumped from the heart against the inner walls of the arteries) or dilation pressure (i.e., exerted by the blood against the inner walls of the arteries when the heart stops contracting in a predetermined short period of time). Pulse rate can also be measured by a typical electronic sphygmometer. As defined, pulse is the regular beating in the arteries caused by the contraction and the dilation of the heart.
A typical electronic sphygmomanometer is advantageous for being compact, having a digital display, and without the cooperation of a stethoscope. Thus, the typical electronic sphygmomanometers are gaining popularity among consumers. The typical electronic sphygmomanometer is characterized in that an air bag is inflated by a pump, then pressure of the air bag is slowly released by a pressure release device, a sensor is deformed due to the pressure change inside the air bag, the differential electrical resistance of the sensor is then measured by the Wheatstone bridge, and finally a blood pressure is displayed.
Referring to FIG. 1, there is shown a block diagram of the typical electronic sphygmomanometer. The sphygmomanometer comprises a processor, an air pump controlled by the processor for pumping air into an air bag until a predetermined pressure is reached, a slow pressure release device is adapted to release pressure of the air bag, and other associated devices (e.g., power, alarm, display, sensor, trigger, fastening device, and quick pressure release device). However, the prior art suffers from several disadvantages. For example, for the sake of portability and the trend of compactness, the bulky pump and pressure release devices are not desirable. Further, strong noise is generated by the pump and the pressure release devices in operation. Hence, a need for improvement exists.